1. Field of the Invention
The present invention relates to a liquid injection system which includes a liquid injector for injecting a liquid from a normal syringe into a patient, and more particularly to a liquid injection system which allows a rodless syringe to be mounted on a liquid injector by a piston adapter.
2. Description of the Related Art
Presently available imaging diagnostic apparatus for capturing fluoroscopic images of patients include CT (Computed Tomography) scanners, MRI (Magnetic Resonance Imaging) apparatus, PET (Positron Emission Tomography) apparatus, ultrasonic diagnostic apparatus, angiography apparatus, and MRA (MR Angiography) apparatus.
When such an imaging diagnostic apparatus is used to capture a fluoroscopic image of a patient, it is occasionally practiced to inject a liquid such as a contrast medium or a saline solution into the patient. There has been put to practical use a liquid injector for automatically injecting a liquid into a patient. A conventional liquid injector will be described below with reference to FIGS. 1 through 3 of the accompanying drawings.
As shown in FIG. 1, normal syringe 10 serving as a liquid syringe comprises cylinder 11 and piston 12 slidably inserted in cylinder 11. Cylinder 11 has slender cylindrical cylinder casing 13. Cylinder casing 13 is closed at a distal end thereof and has central hollow conduit 14 disposed on the closed distal end. Cylinder casing 13 also has cylinder flange 15 disposed on the outer circumferential edge of an opposite open end thereof.
Piston 12 has slender piston rod 17 having piston flange 18 disposed on the outer circumferential edge of an end thereof. Piston head 19 made of an elastic material such as rubber or synthetic resin is mounted on a distal end of piston rod 17. Piston rod 17 is slidably inserted in cylinder 11.
Liquid injector 20 comprises single injection head 21 and two piston actuating mechanisms 22. Single injection head 21 has two recesses 23 for individually holding cylinders 11 of two normal syringes 10. Two piston actuating mechanisms 22 are disposed respectively behind two recesses 23 for holding and moving respective pistons 12 of normal syringes 10.
More specifically, as shown in FIG. 2, piston actuating mechanism 22 has slide rod 25 which is slidable longitudinally and piston presser 26 integrally formed with a front end of slide rod 25 for abutting against the rear surface of piston 12 from behind.
Piston presser 26 has a pair of engaging teeth 27 that are openable and closable, i.e., movable toward and away from each other, horizontally. When engaging teeth 27 are moved toward each other while piston presser 26 is in abutment against piston 12, they engage respective left and right edge portions of the front surface of piston flange 15.
A plurality of types of normal syringes 10 are available for use on liquid injector 20. Normal syringes 10 of those types are made up of components in different sizes and shapes. The liquid injection system which uses liquid injector 20 has as many cylinder adapters 30 provided in readiness for use as the number of different types of normal syringes 10 except for normal syringes 10 of the maximum size.
Cylinder adapters 30 have an outer shape identical to the outer shape of cylinder 11 of normal syringe 10 of the maximum size, and have respective adapter flanges 31 disposed on the outer circumferential edge of an end thereof. Adapter flanges 31 are of the same shape as cylinder flange 15 of normal syringe 10 of the maximum size.
Cylinders 11 of normal syringes 10 of the maximum size or cylinder adapters 30 are placed in respective recesses 23 of injection head 21. If cylinder adapters 30 are placed in respective recesses 23, then cylinders 11 of normal syringes 10 which have a size corresponding to the size of recesses 32 in cylinder adapters 30 are placed in cylinder adapters 30.
In addition to normal syringes 10 described above, there is also available another liquid syringe which comprises rodless syringe 40 as shown in FIGS. 3a and 3b of the accompanying drawings. Rodless syringe 40 has piston 41 comprising a piston head free of a piston rod and having small-diameter piston flange 42 directly formed on an end of the piston head.
Generally, piston flanges 18 of normal syringes 10 are of a larger diameter than the inside diameter of cylinders 11. Piston pressers 26 of liquid injector 20 for holding piston flanges 18 of normal syringes 10 are also of a larger diameter than the inside diameter of cylinders 11.
Therefore, piston pressers 26 of liquid injector 20 cannot enter into cylinder 11 of rodless syringe 40, and hence are unable to directly press piston 41 of rodless syringe 40.
If rodless syringe 40 is mounted on liquid injector 20, then piston 41 thereof is connected to piston actuating mechanism 22 by piston adapter 50.
Piston adapter 50 has adapter rod 51 which is of the same shape as the shape of pistons 12 of normal syringes 10. Piston adapter 50 also has adapter flange 52 disposed on an end of adapter rod 51 and having the same shape as piston flange 18.
Adapter rod 51 of piston adapter 50 has cavity 53 defined in a distal end thereof for receiving piston flange 42 of rodless syringe 40. Flange holder 54 for openably closing cavity 53 is pivotably mounted on adapter rod 51.
The liquid injection system thus constructed operates as follows: Normal syringes 10 of the maximum size are directly mounted on injection head 21. Normal syringes 10 of other sizes than the maximum size are mounted on injection head 21 by respective dedicated cylinder adapters 30. Rodless syringes 10 are mounted on injection head 21 by respective dedicated piston adapters 50 and, if necessary, cylinder adapters 30.
If rodless syringes 10 are used, then flange holders 54 of piston adapters 50 are manually opened, piston flanges 42 are inserted into cavities 53, and thereafter flange holders 54 are manually closed.
Rodless syringes 40 with piston adapters 50 integrally coupled to pistons 41 have an outer shape identical to normal syringes 10. Therefore, rodless syringes 40 can be installed in injection head 21 of liquid injector 20, using cylinder adapters 30, if necessary, in the same manner as with normal syringes 10.
Cylinder 11 of rodless syringe 40 is held in recess 23 of injection head 21 by cylinder adapter 30, and adapter flange 52 of piston adapter 50 that is coupled to piston 41 is held by piston actuating mechanism 22.
Cylinder 11 is connected to the patient by an extension tube (not shown), and piston actuating mechanism 22 is operated to press piston adapter 50. Piston 41 is now pressed, together with piston adapter 50, into cylinder 11, injecting the liquid from cylinder 11 into the patient.
Normal syringes 10 and rodless syringes 40 are available in different types, i.e., a prefilled type wherein the syringe that has been filled with the liquid is shipped and used only once, and a refill type wherein the syringe is filled with the liquid by the operator for repetitive use.
With prefilled-type liquid syringes 10, 40, after pistons 12, 41 are pressed into cylinders 11 for injecting the liquid, there is no need to pull out pistons 12, 41.
Therefore, prefilled-type liquid syringes 10, 40 often have such a structure which makes it easy to press pistons 12, 41 into cylinders 11, but difficult to pull pistons 12, 41 out of cylinders 11.
The liquid injector described above has been invented and applied for patent by the applicant of the present application (see, for example, patent documents 1, 2). The piston adapter described above has been used by the applicant of the present application, but any known documents showing the piston adapter have not been found.
Patent document 1: Japanese laid-open patent publication No. 2002-11096.
Patent document 2: Japanese laid-open patent publication No. 2002-102343.
Liquid injector 20 is capable of injecting the liquid from normal syringe 10 into the patient, and is also capable of using rodless syringe 40 by combining it with piston adapter 50.
Piston adapter 50 has flange holder 54 on the tip end of piston rod 51 for releasably holding piston flange 42. Therefore, when piton rod 51 moves into cylinder 11 of rodless syringe 40 for injecting the liquid from cylinder 11 into the patient, flange holder 54 is no longer accessible for manual operation.
If rodless syringe 40 is of the prefilled type, then since piston 41 pressed into cylinder 11 is not pulled out, piston adapter 50 is not removed from rodless syringe 40 after the injection of the liquid has been completed. Consequently, it is the current practice to throw away piston adapter 50 together with rodless syringe 40 after use.
It would be possible to remove piston adapter 50 from rodless syringe 40 by detaching the extension tube which has connected the patient and rodless syringe 40 to each other, and pulling out piston adapter 50 together with piston 41 to the end of cylinder 11.
However, as described above, though it is easy to press piston 41 into cylinder 11 of prefilled-type rodless syringe 40, it is often difficult to pull piston 41 out of cylinder 11. Actually, therefore, it is hard to remove piston adapter 50 from rodless syringe 40, and even if piston 41 can easily be pulled out of cylinder 11, the process of removing piston adapter 50 from rodless syringe 40 is tedious and time-consuming.
In addition, the need for manually opening and closing flange holder 54 to release and hold piston flange 42 makes piston adapter 50 awkward to handle.